A manual clutch system may be employed selectively to engage or disengage the crankshaft of an engine to the input shaft of a transmission, or, in a front wheel drive, to the input shaft of a transaxle. The principal parts of a typical manual clutch system for vehicles are the driving members, the driven members and the actuating members. The driving members generally present two opposed flat surfaces machined to a smooth finish. One of these smooth surfaces is presented from the flywheel that is secured to the crankshaft of the engine, and the other smooth surface is presented from a pressure plate. The pressure plate may be supported within a cover assembly that is bolted to the flywheel.
The driven members generally include a clutch plate which is operatively connected to the input shaft of the transmission or transaxle. In the majority of such clutch systems, the clutch plate is attached to the input shaft by means of a splined connection between the input shaft and the hub of the clutch plate which permits the hub to adjust its axial position freely along the input shaft and yet assures that the hub will always rotate with the input shaft.
The driving and driven members are normally held in driving contact by spring pressure. The spring pressure may be exerted by a plurality of compression springs or a single diaphragm spring, which is known to the art as a Belleville spring. In any event, the driven members are generally housed within a cover assembly.
The actuating members of a manual transmission normally include: a clutch pedal located for convenient operation by the operator of the vehicle; an assembly from which a throw fork is presented; a connecting means (mechanical and/or hydraulic) which operatively connects the clutch pedal to the throw fork; an adjusting mechanism to balance the desired movement of the throw fork in response to movement of the clutch pedal; and, a clutch release bearing that is supported from a quill which extends outwardly from the transmission or transaxle, housing. The clutch release bearing is slidable axially along the quill in response to movement of the throw fork in order selectively to engage and disengage the clutch plate between the pressure plate and the flywheel.
As is known to the art, and as will be briefly hereinafter reviewed, there are two types of clutch systems--i.e. one that employs a push-type clutch assembly and another that employs a pull-type clutch assembly. In either type clutch assembly, the clutch release bearing must satisfy several design parameters. One design parameter for the release bearing is to assure that the driving engagement effected by the clutch assembly can be released with minimal lost motion of the clutch release bearing relative to its operative contact with both the throw fork and the pressure plate. As such, at least a portion of the release bearing preferably remains in constant contact with the diaphragm spring in preparation for the clutch release. In fact, a modest preload is generally applied to the clutch release bearing to maintain it firmly in contact with the diaphragm spring. As such, the continuous, operative contact between the clutch release bearing and the diaphragm spring requires that at least that portion of the clutch release bearing which contacts the diaphragm spring must be permitted to rotate at engine speed.
Conversely, that portion of the clutch release bearing which engages the supporting quill should not be permitted to rotate in order to simplify not only the interface between the clutch release bearing and the supporting quill but also the interface between the throw fork and the clutch release bearing. Irrespective of whether that portion of the clutch release bearing engaged by the throw fork is permitted to rotate, that same portion of the clutch release bearing must be permitted to slide axially and freely along the supporting quill in order to effect prompt release of the driving connection provided by the clutch, when desired.
Typically, the throw fork presents two fingers which embrace opposed flat engaging surfaces on the nonrotating portion of the clutch release bearing. The flat engaging surfaces are provided to preclude rotation of that portion of the clutch release bearing engaged by the throw fork as a result of the interaction between the fingers on the throw fork and the flat engaging surfaces. This construction is quite sufficient to preclude rotation of the nonrotating portion of the clutch release bearing during operation of the vehicle, but it is not per se adequate to preclude inadvertent rotation of the nonrotating portion of the clutch release bearing when the flat engaging surfaces are disengaged from the throw fork.
In push-type clutch systems, the release bearing is disposed in proximity to some portion of the clutch housing--such as the cover assembly--when the clutch is engaged. Hence, in a push-type clutch system the release bearing may be grounded to the housing member by virtue of a relatively uncomplicated arrangement when one is required to disassemble the clutch assembly. Once the clutch release bearing is grounded, the throw fork can be moved radially to disengage the fingers from the flat engaging surfaces on the release bearing, and that portion which should not rotate will not rotate. This arrangement assures that when the push-type clutch is re-assembled, the flat engaging surfaces on the nonrotating portion of the release bearing will be properly aligned to accept the fingers of the throw fork.
In a pull-type clutch system, however, the relative location of the release bearing with respect to the various other members in the clutch assembly do not readily permit the release bearing to be grounded. As a result, when working with pull-type clutches mechanics must be extremely careful to assure that the nonrotating portion of the clutch release bearing does not rotate when the fingers of the throw fork are disengaged therefrom.